KEY BISCAYNE, Fla. - The Williams sisters resumed their rivalry, and Venus revived it.

Big sis ended a streak of six consecutive losses to Serena, winning 6-1, 7-6 (8) Tuesday in the quarterfinals of the Nasdaq-100 Open.

The upset should help restore some sizzle to a series that has lost much of its luster since the last time Venus won - in the 2001 U.S. Open final before a crowd of 23,023 and a prime-time TV audience.

The stadium at Key Biscayne was only two-thirds full, and rallies by the two sisters were as sloppy as ever. But the upset represented a fresh twist and a psychological breakthrough for Venus, ranked ninth but intent on returning to No. 1.

"For me it's a given," she said. "I feel like I have the talent and the experience. I feel like it's a matter of time."

She has won the Key Biscayne title three times, but not since 2001. Her next hurdle is No. 2-seeded Maria Sharapova in the semifinals Thursday.

"When I get out there, I tell you what, I'm going to do me," Venus said. "Just keep it real."

Said Serena: "Maria should be ready to play, for sure."

In the men's quarterfinals Thursday, No. 1 Roger Federer will play No. 6 Tim Henman, and six-time champion Andre Agassi, seeded ninth, will play fellow American Taylor Dent.

Williams met Williams for the first time since the 2003 Wimbledon final, and the latest chapter in their family feud produced the same awkward shotmaking as in the past. Serena did the splits after one shot; Venus hit a serve that landed short of the net.

"It has always been difficult for me to watch," Agassi said before the match. "I just couldn't imagine what it's like competing against a sibling."

But there was plenty of effort and emotion. When Serena lost the first five games, she took an angry swipe at the hardcourt and mangled her racket, prompting jeers from the crowd.

"Her racket is actually fragile - powerful but fragile," Venus said.

When Venus smacked a crosscourt winner for a 3-2 lead in the second set, she walked to her chair with a glare, her teeth gritted in determination, while Serena admonished herself and screamed a profanity.

"She's definitely a little more fiery than I am," Venus said. "I keep it a little more even-keel."

In the tiebreaker, Serena pushed a forehand into the net to fall behind 9-8, then flung her racket and buried her face in her hands. She sailed a backhand long on match point, and Venus raised her arms in jubilation.

The sisters met at the net and hugged, and Venus consoled her younger sister with a pat on the back. Venus grinned and waved to the crowd, then gestured to Serena and applauded by patting her racket.

"In the last matches, Serena just always played better," Venus said. "She won them. I was happy at least that a Williams won. Obviously I would have loved to have won, but for me it's like the past now."

The defeat ended a 21-match winning streak at Key Biscayne for No. 3-seeded Serena, the three-time defending champion.

"There was nothing I could do in the first set, but I had plenty of chances in the second," Serena said. "We should still be out there."

The sisters took the court at 8:30 p.m., Serena wearing a fuchsia body suit and Venus in a more conservative black and white dress. Serena foot-faulted twice in her first service game, perhaps a sign of nerves, and was soon talking to herself.

"Why would you do that?" she said after one errant shot.

"The first set for me was fantastic," Venus said.

Venus smacked winners into the corners and scrambled after shots beyond the reach of most players, surprising Serena at least once when the ball came back. But Venus also had seven double faults and 30 unforced errors while converting just three of 12 break-point chances, and Serena was no sharper.

Most of the drama came in the tiebreaker. Serena saved one match point when Venus mis-hit a backhand for 6-6. Venus then twice saved set points with backhand winners, the second kissing the baseline for 8-all.

Two points later, Venus had a big win.

"It definitely felt nice," she said.